Parker, a forest ecologist at the Smithsonian Institution, has spent the past 22 years on a research project so repetitive, so time-consuming, that it impresses even researchers with the patience to count tree rings. Since 1987, he and a group of volunteers have embraced thousands of trees, slipped a tape measure behind them, and wrapped it around to measure the trees' girth.

This year, after about 250,000 hugs between them, the work paid off. Parker's data, which showed the trunks gradually fattening over time, indicated that many of the trees were growing two to four times faster than expected. That raised questions about climate change's impact on the age-old rhythms of U.S. forests.

…Last year, when Parker analyzed the mountain of data his team had collected, he found something surprising: Their trees were adding bulk at a surprisingly fast rate.

Parker said the best explanations for this all seemed to relate to climate change. Temperatures in the area have risen by three-tenths of a degree; the growing season has lengthened by 7.8 days; and the amount of carbon dioxide in the atmosphere has risen. All of those might speed up photosynthesis, the engine of tree growth.